No... he's being serious.
If you run Stras into the ground... you sap every last bit of value out of him and you get massive return on your investment. From an economist point of view... that likely would be the right way to do it.
I don't think so. An economist would argue for maximizing the return on the investment over the lifetime of the investment - running him into the ground so that you win the WS this year and he never pitches again is leveraging the long-term value of the good to maximize the one-year return - like taking a second mortgage on your house to put it in the stock market. It's a higher-risk play with higher upside, but risks diminishing the overall return on investment. That said, if it works and you don't hurt his longer-term potential, it's the best possible outcome - it all boils back down to how you judge the risk.
An economist would probably have argued for the strategy they are following - maximize his $$ return this year by having him pitch in games that are less likely to draw significant numbers of fans, then shut him down for those games where the team will sellout anyway (playoffs) and hedge the risk to his longer-term value as best you can. From an overall efficiency vs. risk point of view, shutting him down now is probably the right call. But I don't think Rizzo is thinking about it in a dollars-and-cents way. You could certainly start to monetize it down to marginal Nats cost per Stras start (his salary) vs. marginal Nats return per Stras start (average difference in attendance, marginal jersey sales, some pro-rated figure for Stras' presence on the roster leading to higher attendance even at non-Stras games, etc.) to figure out how to maximize revenue inflow vs. invested salary. But that would be BOOOOORING.